1. Field of the Invention
The present invention relates to a vertical line multiplication method for a high-resolution camera and a circuit therefor. More particularly, the present invention relates to a vertical line multiplication method and circuit for multiplying the number of vertical lines of a video signal which is imaged by use of 4 charge coupled devices (CCDs) to transform the signal into another video signal having a higher resolution by controlling writing and reading of signals to and from a memory.
2. Description of the Related Art
Recent experimentation with digital broadcasting of high-definition television (HDTV) and the commercialization of "wide" televisions having an aspect ratio of 16:9 have created the need for a charge-coupled device (CCD) camera which supports the imaging techniques of various standards, i.e., HDTV, wide TV and the NTSC standard now in common use.
Generally speaking, camera performance improves and equipment costs rise as the number of charge-coupled devices increases. commercially available cameras for home use usually have employed a single-plate CCD, while a three-plate CCD has been produced for business use such as at a broadcasting station.
A four-plate CCD camera, having a much more complex signal processing structure than the triple-plate CCD camera, offers excellent performance and supports the high resolution of the HDTV standard.
Here, the "HDTV standard" includes a high vision standard developed in Japan, a GA-HDTV standard proposed by the Grand-Alliance (GA) committee in the United States, an ATV standard and a HD standard.
The high vision standard has 1035 effective vertical lines among 1125 total lines and 1920 effective pixels among 2200 total pixels in each horizontal line. The GA-HDTV standard has 1035 effective vertical lines among 1125 total lines and 1258 effective pixels among 1440 total pixels in each horizontal line. The ATV standard has 1080 effective vertical lines among 1125 total lines and 1920 effective pixels among 2200 total pixels in each horizontal line. The HD standard has 1024 effective vertical lines among 1125 total lines and 1008 effective pixels among 1200 total pixels in each horizontal line.
A household HDTV camera employing a 4-CCD technique has to have advantage of being compatible with other formats, i.e., existing NTSC and wide TV formats while being low-cost.
Meanwhile, a household NTSC standard CCD currently being used cannot be used for a high vision standard camera since the number of effective vertical lines of the NTSC CCD is only 485, which is shorter than half of the effective vertical lines, i.e., 1035, of the high vision standard. Also, even though a PAL CCD has enough effective vertical lines, a PAL CCD cannot be used for a high vision standard camera either since the requirement of the number of horizontal pixels is not satisfied.
To overcome these problems, it is possible to use a general purpose CCD having 630,000 pixels (726 vertical lines and 858 horizontal pixels) for a
hand trimming compensation as a CCD for a household HDTV camera, and control the CCD so that some part of the CCD is used depending on a standard, as shown in FIG. 1.
FIG. 1 shows the available area of a CCD for each standard: 16:9 high vision, 16:9 NTSC for wide TV and 4:3 SD (standard definition) standards.
For its compatibility, the household 4-CCD camera shown in FIG. 1 uses 808H.times.518V, 754H.times.485V and 566H.times.485V of the total number of pixels for the 16:9 high vision, the 16:9 NTSC, and the 4:3 SD, NTSC standards, respectively.
FIG. 2 illustrates the structure of an optical system employing a 4-CCD design. The optical system includes first through third optical lowpass filters (LPFs), a prism, and four CCDs fixed to the prism.
Here, a light passing through a lens passes through the optical LPF 1 before being incident on the prism 10. When incident light is sampled by use of the CCDs, an aliasing may be present due to the limitation of the number of pixels. Thus, the optical LPF 1 attenuates the aliasing component which exceeds the Nyquist frequency among the incident light.
The light incident on the prism 10 is divided into green (G), red (R) and blue (B) signals according to their wavelengths at the boundary of the prism. Further, the G signal is divided into G1 and G2 signals before entering the CCDs. Light divided into the blue (B) signal is incident on the optical LPF 2 and then passes through to the B CCD, whereas the light divided into the red (R) signal is incident on the optical LPF 3 and then passes through to the R CCD. Two CCDs (G1 CCD and G2 CCD) are provided for the G signal because the G signal has the highest ratio (70% for HD standard) among the Y signal distribution and because it is highly sensitive. Meanwhile, the G1 CCD and the G2 CCD are disposed so that the G2 CCD outputs a video signal which is shifted by one horizontal line from a video signal output by the G1 CCD.
On the other hand, the light incident on the G1 CCD or G2 CCD has about twice the bandwidth as that of the R CCD or the B CCD, due to the characteristics of the optical LPFs.
FIG. 3A shows the frequency characteristics of the first through third optical LPFs. The first LPF directly affects the G1 and G2 signals, but the second and third LPFs affect only the B and R signals, respectively, since they are located in front of the R CCD and the B CCD. Here, Fn denotes a normalized maximum frequency that can be recognized as a signal during the sampling of light in CCDs. As a result, the frequency characteristics of the light incident on the B CCD can be obtained by performing an inner product operation of the frequency characteristics of LPF 1 and that of LPF 2. Also, the frequency characteristics of the light incident on the R CCD can be obtained by performing an inner product operation of the frequency characteristics of LPF 1 and that of LPF 3. The resultant frequency characteristics of the light incident on the R CCD and the B CCD is shown in FIG. 3B.
FIG. 4 is a block diagram of a signal processing system for transforming an NTSC signal output by a CCD into an HDTV signal, which is disclosed in ITE Technical Report, Vol. 19, No. 20, pp 53-58, Mar. 17, 1995.
Signal processing is digitalized in the circuit shown in FIG. 4 to process various broadcasting standards, in other words, to enable imaging in different modes including NTSC 16:9 and NTSC 4:3 modes as well as a high-definition television mode.
In the case of a high vision camera employing an exclusive CCD with more than 10.sup.6 pixels, the digitalization of its circuit has made little progress since the horizontal transfer clock of the CCD is higher than 37 MHZ and its signal processing is difficult. However, when a PAL hand trimming compensation 4-CCD is used, the digitalization of its circuit is possible since the horizontal transfer clock of the CCD is as low as about 16 MHZ and its signal processing is easy.
In FIG. 4, G1 and G2 signals output from two G CCDs (G1 CCD and G2 CCD, respectively) in accordance with the 16 MHZ clock signal, are converted into digital signals and supplied to a horizontal interpolation circuit 14 through a contour correction circuit 12.
The horizontal interpolation circuit 14 interpolates pixels in the horizontal direction and outputs the interpolated signal in accordance with a 32 MHZ clock signal.
The G channel vertical line multiplication circuit 16 rearranges the signals originated from the G1 CCD and the G2 CCD which are being shifted one horizontal line vertically so that they are in time with a displaying order, and compresses the rearranged signal in time. Afterwards, the 6 channel vertical line multiplication circuit 16 outputs the compressed signal in accordance with a 64 MHZ clock signal as a wide bandwidth G signal.
Here, the clock speed doubles after a horizontal interpolation and doubles again after a vertical line multiplication to be four times the input clock speed.
A G-Y transformation circuit 18 combines the wide bandwidth G signal and a G.sub.L -Y.sub.L signal from the multi-speed transformation circuit 26 to output a wide bandwidth Y signal.
On the other hand, a lowpass filter (LPF) 20 carries out lowpass filtering of the analog-to-digital converted G1 and G2 signals to output the low frequency components G.sub.L of such signals.
A color matrix circuit 22 receives the G.sub.L signal output by the LPF 20 and analog-to-digital converted R and B signals, generates color difference signals, R-Y.sub.L, G-Y.sub.L and B-Y.sub.L, and outputs such color difference signals.
A vertical line interpolation circuit 24 interpolates pixels in the vertical direction with respect to each of the color difference signals, R-Y.sub.L, G-Y.sub.L and B-Y.sub.L.
The multi-speed transformation circuit 26 inputs the interpolated color difference signals and carries out vertical line multiplication.
Afterwards, the vertical-line-multiplicated signals R-Y.sub.L and B-Y.sub.L are converted into analog signals in accordance with a 32 MHZ clock signal.
Therefore, a household camera which complies with an HDTV standard by using four PAL hand trimming compensating CCDs, carries out a horizontal interpolation and a vertical line multiplication for a G signal, but only a vertical line multiplication for R and B signals which have half the amount of G signal information, as shown in FIG. 4.
Meanwhile, the detailed configuration of the vertical line multiplication circuit is not disclosed in the above literature.